COGS 17 Lecture Notes - Lecture 8: Ossicles, Tectorial Membrane, Basilar Membrane

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Lec 5A - Audition
Sound waves
Frequency = number of cycles/second (Hz)
Per speed at which molecules of medium (air) oscillate
Phase = place in cycle of condensation and rarefaction
Peak and trough
Amplitude = distance a given molecule of medium (air) travels during its
oscillation
Auditory reception
Pinna - external ear. Individually distinct as fingerprints
Auditory canal ends in eardrum
Eardrum - thin membrane, also called tympanic membrane
Ossicles - smallest bones, libra system leads to cochlea
Cochlea - neurons that react to vibration in ear
The middle ear
Eardrum - connects to auditory ossicles (bones): malleus, incus, and
stapes
Jointed together
Malleus pushed up against tympanic membrane
Stapes up against the oval window (membrane) - much
smaller than tympanic
Ossicles function is to convert large vibrations of big tympanic
membrane into smaller, but more powerful vibrations of oval
window
Overcomes impedance (resistance that a medium puts
up to propagate sound) mismatch between air and
cochlear fluid inside the cochlea
Vibrations
The cochlea
Coiled into a snail shape
Upper, lower and middle chamber
Middle chamber → organ of corti
Where neurons are that react to vibrations in ear
Basilar membrane: floor of middle chamber and organ
of corti, on which the hair cells (receptors) sit
Tectorial membrane: within the middle chamber, top of
organ of corti
Organ of corti
Hair cells - auditory receptors
Stand between tectorial membrane above, and basilar
membrane blow
As membranes vibrate, cilia (hairs) are bent → release
NT
Transduction in hair cells is potassium (K+) based (no Na+)
Cochlear fluid is rich in potassium
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Document Summary

Per speed at which molecules of medium (air) oscillate. Phase = place in cycle of condensation and rarefaction. Amplitude = distance a given molecule of medium (air) travels during its oscillation. Eardrum - thin membrane, also called tympanic membrane. Ossicles - smallest bones, libra system leads to cochlea. Cochlea - neurons that react to vibration in ear. Eardrum - connects to auditory ossicles (bones): malleus, incus, and stapes. Stapes up against the oval window (membrane) - much smaller than tympanic. Ossicles function is to convert large vibrations of big tympanic membrane into smaller, but more powerful vibrations of oval window. Overcomes impedance (resistance that a medium puts up to propagate sound) mismatch between air and cochlear fluid inside the cochlea. Where neurons are that react to vibrations in ear. Basilar membrane: floor of middle chamber and organ of corti, on which the hair cells (receptors) sit. Tectorial membrane: within the middle chamber, top of organ of corti.

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